Printing devices that feed sheets of a recording paper stacked in a feeding cassette to a printing position one sheet at a time, where an image-recording unit prints an image on the paper, are well known in the art. This type of printing device generally includes a feeding roller for repeatedly feeding the topmost sheet of recording paper stacked in the feeding cassette along a conveying path one sheet at a time. Once the feeding roller has fed the sheet of paper along the conveying path to a conveying roller, the conveying roller continues conveying the paper to the printing position. The printing device prints images on the recording paper using a recording head that ejects ink onto the paper, for example.
Since the feeding distance from the cassette to the conveying roller is fixed, it should be possible to feed the recording paper appropriately from the cassette to the conveying roller by determining the rotational amount required by the feeding roller. However, in reality, the feeding roller sometimes slips over the recording paper. The amount of slippage varies according to wear on the feeding roller, ambient temperature and humidity, and the type of recording paper. If the amount of slippage is large, the recording paper may not reach the conveying roller simply by rotating the feeding roller a rotational amount equivalent to the feeding distance. If the feeding roller stops before the recording paper has reached the conveying roller, the conveying roller cannot begin conveying the recording paper, leaving the paper stuck in the conveying path. In such a case, the user must open the cover of the printing device to extract the recording paper from the conveying path.
A variety of methods have been proposed to ensure the recording paper reaches the conveying roller. For example, a printing device disclosed in Japanese Patent Application Publication No. 5-155086 adjusts the rotational amount of the feeding roller based on the thickness of the recording paper. Further, a printing device disclosed in Japanese Patent Application Publication No. 9-52421 includes a positional sensor for detecting passage of the leading and trailing edges of the recording paper and calibrates the rotational amount of the motor for feeding subsequent sheets of recording paper, based on the rotational amount of the motor required to convey the trailing edge of the recording paper past the positional sensor after the leading edge was detected.